Antenna



Oct. 25, 1949. I 4 H. J. RIIBLET J 2 ANTENNA Filed April 26, 1944 -QINVENTOR.

HENRY J R/BLET Patented Oct. 1?.5, 1949 ANTENNA Henry J. .Riblet,Cambridge, Mass., assignor, by mesne assignments, to the United Statesof America as represented by the Secretary of War Application April 26,1944, Serial No. 532,793

Claims. 1 This invention relates to an antenna and more particularly toa directional type antenna adapted for use generally in high frequencycommunication systems. An antenna of this character will have a widevariety of applications,

particularly in instances where size and weight ject contemplates anantenna of this character adapted for service in difiicult locations.Other objects involve considerationsof :small size, light weight andease of manufacture.

The invention provides an end-fire type antenna mounted directly on anassociated feeder transmission line, in this instance shown as a coaxialcable. The antenna construction comprises a plurality of dipolesextending outwardly from the cable. Any reasonable number of dipoles,such as 2, 3, or 4, may be used with the 1 invention, the number useddepending generally upon the radiation pattern desired. In theillustrated form of the invention, two dipoles areprovided. The dipolesare disposed a half wave length apart so that maximum radiationtherefrom is directed generally along an axis normal to the plane of thedipoles. A parasiti reflector may be mounted on the cable and spacedbehind the dipoles in order to provide :a predetermined uni-directionalradiation characteristic, and to increase the antenna gain in thedesired direction. The dipoles are excited in phase with-each other bymeans of adjustable probes extending into the region of propagationwithin the cable. Th probes may physically contact the central cableconductor, or they may be spaced a predetermined distance therefrom toprovide capacitive coupling if desired. The dipoles because of theirsmall size and shape may easily be weatherproofed by encloseure in asuitable energy transparent housing.

A modification of the invention involves use of a plurality of the abovedescribed dipole units to make up an antenna array. For example, anumber of such units may be mounted in predetermined spaced relation ona coaxial cable or hollow wave guide, the spacing and probe adjustmentused depending generally upon the radiation pattern desired. Such anarray has been 2 :found to give an unexpectedly high :gain for anend-fire type antenna.

In the drawing, Fig. 1 is a perspective view of the dipole unit; Fig. 2is a plane view of the invention showing the dipole unit and a reflectormounted in position on a coaxial cable, the dipole unit being enclosedin :a suitable transparent housing; Fig. 3 is a sectional view on theline 33 of Fig. 2; Fig. 4 is a fragmentary cutaway view of a portion ofFig. '2; Fig. 5is a view showing the approximate radiation patternprovided by the illustrated single unit antenna; and Fig. 6 is amodification showing use of a plurality of dipole unit in an array.

Referring now to Fig. .1 (lower left-hand scorner) the dipole unitcomprises a metallic central collar :5 of proper diameter tosnuglyfitover the outer conductor of an associated feeder transmission.line. Spaced parallel dipole supporting :arms 6 and I extend laterally:from collar 5 and carry at their ends dipole sections 8 and 9. .As will:be understood, sections 8 and 9 comprise one dipole of the unit.

A second dipole comprising spaced arms in and H and associated section-sl2 and I3 extends in a symmetrical manner from the opposite side ofcollar 5. If more than two dipoles are used, they may be spaced atregular intervals about the collar. Preferably the collar, arms andsections are cast as an integral metallic zunit, aluminum .being aparticularly good material for this purpose.

Section 9 of the first dipole has an integral extension l5 projectingsomewhat into the space between arms 6 and 1. Extension l5 has :anaperture centrally located with respect to arms 5 and 1. An adjustableprobe I6 is threaded through said aperture, the probe being arranged toextend inwardly to a predetermined position within the space enclosed bycollar 5. Ashallow recess may be provided in collar 5 to insure suitableclearance between the collar and probe I6. Similarly, section It of theopposite dipole has .an extension I! and an associated probe I8.

While it has been found that the dimensions of the above-describeddipole unit are .not particularly critical, best results ordinarily areobtained when the effective distance between the two dipoles, i. e. thedistance between extensions I 5 and I1, corresponds generally to a halfwave length. This is the distance customarily used in antenna arrays tominimize radiation in the plane of the array. The size of collar 5, of.course, is dependent upon th diameter of the associated transmissionline, the diameter being usually less .practice for parasiticreflectors.

antenna. an additive manner to increase the intensity of than a quarterwave length. Consequently, the physical length of supporting arms 6, andIO, II will be somewhat less than a quarter wave length.

- Dipole sections 8, 9, l0, and I, as shown in the drawing, havegenerally a circular configuration. It is to be noted that this circularshape is provided generally to simplify manufacture, and also to reducethe size of the assembly.

Referring to Fig. 2, a dipole unit 20 is rigidly mounted on the end of acoaxial cable 2|, solder or other suitable means being used to insure agood electrical and mechanical connection. Although a coaxial cable maybe preferred in most instances, it will be understood that the dipoleunit could be used with a hollow wave guide type transmission line, ifdesired. Spaced apertures 22 (Fig. 4) are provided in the outer cableconductor in aligned relation with probes l6 and I8. The probes enterthe space within the conductor through the apertures, and may beadjusted radially for the coupling desired. Thus the probes may contactthe central cable conductor for direct coupling, or they may be spacedtherefrom for capacitive coupling. After adjustment of the probes, thehead ends thereof can becut off at extensions l and I1 (best shown inFig. 3). Solder may be used at the extensions to insure a goodelectrical connection and to prevent subsequent displacement of theprobes.

Also mounted on cable 2| is a metallic plane reflector 25, the diameterof reflector 25 being somewhat greater than that of the dipole unit.Reflector '25 is preferably in the form of a circular disc, a supportingcollar 26 being associated therewith to rigidly mount the reflector oncable 2|. The surface of disc 25 facing dipole unit 20 is spacedtherefrom to provide a desired energy distribution pattern in accordancewith the usual As is well known, a metallic reflector positioned behinda radiatin antenna is excited thereby. Currents induced in such areflector cause radiation therefrom which has an effect on the radiationpattern 7 of the antenna proper. Wave energy radiated by the reflectorin the direction of the antenna generally is in phase with the directradiation of the Therefore, the two fields combine in radiation in thatdirection. Good antenna gain is thereby obtained. Conversely, respectiveradiations in the opposite direction are generally out of phase, the twocombining therefore in a subtractive manner to substantially eliminateradiation in that direction. Thus the radiation produced by such anantenna-reflector combination is uni-directional, the line of maximumradiation corresponding generally to the axis of cable 2| extendedbeyond the dipole unit.

A cup-shaped housing 30, which is transparent to the radiated energy,may enclose dipole unit 20 and the associated end of cable 2|. Housing30, which may be made of such materials as are commonly known by thetrade names Plexiglas or Lucite, serves to weather-proof the unit aswell as to seal the end of cable 2| in a pressure-proof manner.

The approximate energy distribution pattern obtained from the two dipoleantenna with a reflector is shown in Fig. 5. The substantiallypear-shaped pattern shown is generally circular in section. Otherdistribution patterns may be obtained through appropriate choice of thenumber of dipoles provided and their disposition about the conductor.

An array comprising a plurality of dipole units is shown in Fig. 6.Here, a number of units 35 are arranged longitudinally in spacedrelation on coaxial cable 36. The units are mounted on the cable asabove described, the dipoles of each unit being excited in phase. Theaxial distance between units depends generally upon the radiationpattern desired, the distance usually being the order of a quarter wavelength. Other spacings may be used as long as the distance issubstantially less than a half wave length. For instance, one-third wavelength spacing has been used. As is Well understood, the radiationpattern and operation of an array depend upon the phase relationshipsbetween the various units of the array. In such an array, desiredphasing is obtained through cooperative effects of the physical spacingof the units and adjustment of the probes. In practice, the spacing maybe fixed, and the probes are adjusted to obtain the desired phaserelationships, as determined by maximum gain in the desired directions.Here again, the antenna may be enclosed in a suitable housing forweatherproofing, and to provide a seal if the system is pressurized.

As one example of such an array, 18 dipole units have been foundespecially satisfactory in an array adapted for use at wave lengths ofthe order of 10 centimeters. The dipole units may be spaced and excited,in the usual manner, so that there is a progressive phase differencebetween adjacent units generally equal in cycles to the spacing betweenthe units in wave lengths. Thus if the adjacent units are a quarter wavelength apart, a phase difference of between units generally is used. Itmay be preferred to vary this arrangement slightly in accordance withthe suggestion of W. W. Hansen and J. R. Woodyard (Proc. I. R. E., vol.26, p. 333, March 1938), wherein the phase difference between. adjacentunits is increased by 1r/1l radians, where n is the number of unitsused. Thus the length (in wave lengths) of the array will be a half wavelength in excess of the free space electrical length (in wave lengths).

The transmission line associated with such an array may be terminated inany desired manner, such as by absorbing arrangement, or by a simplereflecting termination. The latter may be a short-circuited terminationconstituting a stub support. The antenna units introduce enough standingwaves into the line so that the additional standing waves arising fromthe short-circuited termination are not substantial. The entire standingwave pattern may be matched as a whole at theinput end by a suitabletransformer. The dipoles have been found to, operate most efficientlywhen the probes thereof are soadjusted as to permit approximately 10% ofthe energy to reach the terminating. end of the line, Under thiscircumstance, all dipole units are in effective operation.

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent is:

1. An integral metallic antenna construction for use with a wave guideor coaxial cable, said construction comprising an inner supportingcollar carried by said wave guide or outer conductor of said coaxialcable, a plurality of pairs of arms extending outwardly from saidcollar, a section of a dipole carried at the end of each arm with a pairof arms supporting a dipole, said arms'and dipoles all lying generallyin a plane normal to the axis of said guide or cable, a probe carried bythe end of one section of each dipole, said probe extending inwardly andbeing adapted to clear said collar and extend into the region ofpropagation within the said guide or cable through aligned aperturestherein, whereby said dipoles are excited in phase.

2. The combination of claim 1 having two diametrically opposed dipoles,the efiective distance between said dipoles being a half wave lengthwhereby the direction of maximum radiation lies along the extended axisof said wave guide or cable.

3. The combination of claim 1 having two diametrically opposed dipoles,the effective distance between said dipoles being a half way length, anda parasitic reflector mounted on said wave guide or cable, the surfaceof said reflector being parallel to the plane of said dipoles and spaceda predetermined distance therefrom.

4. In combination with a wave guide or coaxial cable, an end-fireantenna array of the character described comprising a plurality ofdipole devices defined in claim 1 mounted in spaced relation on saidwave guide or coaxial cable, the spacing between adjacent devices andthe adjustment of the probes of each device being such as to providepredetermined phase relationships in the successive dipole devicesduring operation of the array, thus to provide a predetermined energydistribution pattern.

5. An end-fire antenna array in combination with a feeder wave guide orcoaxial cable, said array comprising a plurality of dipole units mountedin spaced relation on said wave guide or coaxial cable, each dipole unitincluding an inner supporting collar carried by said guide or cable, twopairs of arms extending diametrically outward from said collar, asection of a dipole carried at the end of each arm with a pair of armssupporting a dipole, said arms and dipoles lying generally in a planenormal to the axis of said guide or cable, a probe carried by the end ofone section of each dipole and extending inwardly to the region ofpropagation within said guide or cable through aligned aperturestherein, the spacing between adjacent units and the adjustment of saidprobes of each unit being such as to provide predetermined phaserelationships in the successive dipole units during operation of thearray, thus to provide a predetermined energy distribution pattern.

HENRY J. RIBLET.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,931,980 Clavier M Oct. 24, 19332,187,618 Gerhard Jan. 16, 1940 2,298,449 Bailey Oct. 13, 1942Certificate of Correction Patent N 0. 2,485,920 October 25, 1949 HENRYJ. RIBLET It 1s hereb certlfied that error appears in t correction asfofiows:

he above numbered patent requiring Harry J. Riblet read Henry J. Riblet;

ad with this correction therein that the the record of the case in thePatent Oifice. Signed and sealed this 28th day of February, A. D. 1950.

THOMAS F. MURPHY,

Certificate of Correction Patent No. 2,485,920

October 25, 1949 HENRY J. RIBLET It is hereb certified that correctionas foh error appears in th ows:

Harry J. Riblet ad with this correc the record-of the case in the PatentOffice lgned and sealed this 28th day of February, A. D. 1950.

read Henry J. Rz'blet; tion therein that the THOMAS F. MURPHY,

Assistant C'ommz'ssz'oner of Patents.

